My system tray icons appear to be little square boxes instead of icons in login screen. On my user desktop however, they show up as the correct icons. This appears to have started after playing with Ubuntu Tweak. Everything else is working fine. Any ideas to get those little icons looking like little icons in the login screen? Thanks
Open a terminal (Ctrl Alt T)
Now you need to reset the Ubuntu tweak tool.
If this does not work you can try to reinstall ubuntu-desktop
First login to tty(Ctl Alt F1)
After you login to the tty type
sudo apt-get install --reinstall ubuntu-desktop
(you can also run this on " safe mode"
sudo apt-get aptitude install --reinstall ubuntu-desktop)
After this completes reboot